1. Field of the Invention
The present invention relates in general to video compression/expansion apparatus for video cassette recorders (VCRs), and more particularly to a video compression/expansion apparatus for a home digital VCR which is capable of, utilizing a video compression/expansion device, compressing a still video signal as well as a motion video signal to record the compressed video data on a video tape and expanding the compressed video data recorded on the video tape to play back the original video signals.
2. Description of the Prior Art
Referring to FIG. 1, there is shown a schematic block diagram of a conventional video compression apparatus. As shown in this drawing, the conventional video compression apparatus comprises an analog/digital (A/D) converter 1 for converting an analog video signal inputted therein into digital video data, a memory 2 for storing the digital video data From the A/D converter 1, a video compression/expansion device 15 for compressing the video data stored in the memory 2 and expanding the:compressed video data, a central processing unit (CPU) 4 for controlling read and write operations of the compressed data from the video compression/expansion device 15, a compressed data memory 5 for storing the compressed data from the video compression/expansion device 15 under the control of the CPU 4, and a digital/analog converter 17 for converting the digital video data from the A/D converter 1 or the memory 2 into the original analog video signal and outputting the converted analog video signal externally.
In operation, upon receiving the analog video signal, for example, included in a television (TV) signal, the A/D converter 1 converts the received analog video signal into digital data, which is then stored in the memory 2 in the unit of field or frame. The digital video data stored in the memory 2 is inputted by the video compression/expansion device 15 through a pixel bus interface 151 thereof. The video compression/expansion device 15 compresses the inputted video data on the basis of a JPEG algorithm and outputs the compressed video data to the compressed data memory 5 through a host bus interface 152 thereof under the control of the CPU 4 so that the compressed video data can be stored in the compressed data memory 5 as needed,
The compressed video data is read from the compressed data memory 5 under the control of the CPU 4 and then applied to the video compression/expansion device 15. Upon receiving the compressed video data from the compressed data memory 5, the video compression/expansion device 15 expands the compressed video data into the original state and stores the expanded video data into the memory 2. The expanded video data stored in the memory 2 is converted into the original analog video signal by the D/A converter 17, which then outputs the converted analog video signal to a monitor.
However, the conventional video compression apparatus is desirable to compress a still video signal under the control of the CPU, but has a disadvantage in that it can hardly compress a video signal included in a TV signal of a NTSC system in a real. Lime manner since the CPU has a low processing speed.
Referring to FIG. 2, there is shown a schematic block diagram of a conventional video expansion apparatus employing the video compression/expansion device 15 in FIG. 1. As shown in this figure, the conventional video expansion apparatus comprises a demodulator/error corrector 12 for demodulating compressed video data read from a video tape 11 and correcting an error of the demodulated video data, a deformatter 13 for extracting only actual video data from output data from the demodulator/error corrector 12, and a first buffer 14 for storing the extracted video data from the deformatter 13 temporarily.
The video compression/expansion device 15 is provided in the conventional video expansion apparatus to expand the video data stored in the first buffer 14.
Also, the conventional video expansion apparatus comprises a second buffer 16 for storing the expanded video data from the video compression/expansion device 15 temporarily.
The D/A converter 17 in FIG. 1 is also provided in the conventional video expansion apparatus to convert the video data stored in the second buffer 16 into an analog video signal and output the converted analog video signal to display it.
In operation, upon receiving the compressed video data read from the video tape 11, the demodulator/error corrector 12 demodulates the compressed video data into the original state and then corrects the error of the demodulated video data which occurred on the video tape 11 . The deformatter 13 extracts only the actual video data from the output data from the demodulator/error corrector 12 and then stores the extracted video data into the first buffer 14 temporarily.
Thereafter, the video data stored in the first buffer 14 is expanded into the original state by the video compression/expansion device 15 and then temporarily stored in the second buffer 16. The video data stored in the second buffer 16 is converted into the analog video signal by the D/A converter 17, which then outputs the converted analog video signal so that the analog video signal can be displayed in a desired scanning manner.
Noticeably, in order to effectively expand the video data, the conventional video expansion apparatus employing the video compression/expansion device 15 may greatly be divided into three parts in which different clocks are used, or first to third parts as shown in FIG. 2. For this reason, the three parts must be synchronous with one another to real time-process the operations of reading the compressed video data from the video tape 11, expanding the read, compressed video data and displaying the expanded video data. In this connection, the conventional video expansion apparatus has a disadvantage, in that it is impossible to synchronize the clock used in the second part with the clocks used in the first and third parts utilizing a phase locked loop (PLL) since the compressed video data stored in the first buffer 14 is variable length coded data.